During the manufacturing of electronic devices, individual integrated circuits generally undergo testing for functional and other defects using automated test equipment. The tests sometimes are performed at various temperatures; for example, “hot” and “cold” testing. During such tests, it may be important to keep the junction temperature of the integrated circuit being tested (“Device Under Test”—DUT) substantially close to the selected temperature set points.
To maintain the temperature of the DUT at selected temperature set points, an automatic thermal control equipment handler (ATC) may be used. In general, the ATC attempts to maintain a constant temperature set point before test (sometimes called “T-soak”) as well as actively cool the DUT during execution of the test pattern(s). The degree of cooling is modulated during the test as a function of the DUT temperature and the electrical power consumed by the DUT. Owing to the fact that this thermal control has a dynamic behavior, the temperature of the DUT is difficult to control. Specifically, the temperature of the DUT may undershoot (e.g., due to overcooling) or overshoot (e.g., due to less cooling) the desired set point. As a result, the DUT may be under-tested giving rise to potential quality issues, or may be over-tested affecting yield, reliability, and/or other issues.
A thermal diode disposed at the edges of the DUT is sometimes used to determine whether temperature overshoot or undershoot of the DUT occurred during a test. The diode is read only after the conclusion of a test and the reading is then compared to predetermined guardbands (e.g., minimum and/or maximum temperature limits). Due to the location of the diode, the estimation of the temperature generally can never be close to the true temperature at the core of the DUT. In addition, the diode is measured at the end of a test rather than during execution of the test, at which point the temperature of the DUT may have changed. Furthermore, analyzing such data after the test is completed adds a significant amount of additional processing time, which may be incompatible with high-volume manufacturing needs. As a result of these problems, the cooling of the DUT is usually very conservative and the guardband(s) are usually sizeable to ensure that passing DUT meet the desired standards.